Agricultural sprayers are used by farmers and contractors to apply pesticides and other nutrient-containing solutions to crop fields. Sprayers can be mounted to, or towed by, a tractor or other suitable vehicle or may be self-propelled with an integrated means of propulsion and a driver's cab. The sprayer machine typically includes a storage tank for the liquid to be applied, the tank being filled as required by the operator.
The liquid is applied to the field by a number of liquid application devices, typically spray nozzles, which are mounted in a spaced relationship along the length of a boom which, itself, is mounted to the sprayer vehicle. The nozzles are each connected to the storage tank by liquid delivery means comprising various pipes, valves, pumps and other plumbing. The liquid is atomised by the nozzles and applied to the crop in a jet of mist for example.
Applicator booms typically comprise a centre frame which is mounted to a chassis or machine frame at the rear. An adjustable linkage may be employed to permit the boom to be raised and lowered with respect to the ground. Side assemblies are attached to the left- and right-hand sides of the centre frame in a hinged manner so that the boom, in an operating configuration, extends transversely with respect to the forward direction of travel and, in a transport configuration fold with respect to the centre frame so as to extend longitudinally forward alongside the tank.
Each side assembly typically comprises more than one boom section, wherein adjacent sections are connected by a hinged joint which permit the sections to be folded 180 degrees around an upright hinge axis when in the transport configuration.
Respective hydraulic cylinders connected between adjacent mutually-hinged sections serve to control the folding and deployment thereof.
The length of the overall boom determines the operating width of the sprayer. Driven by economies of scale, there is a growing demand for sprayer manufacturers to produce machines with longer spray booms. However, increasing the boom length significantly increases the risk of structural failure due to the increased stress placed upon the hinges and joints caused by natural vibrations and oscillations which pass from the spray vehicle along the boom. Moreover, the amplified oscillations along the boom, left uncontrolled, can lead to uneven application of pesticides.
The centre frame is, on larger machines especially, suspended relative to the chassis to permit pitch, roll and yaw movement of the boom and reduce bending stresses in the boom caused by movement of the machine especially over uneven ground. Spring and damper mechanisms provided on the centre frame serve to control these movements.
Despite such efforts to reduce the stresses caused by boom oscillations, boom lengths are, today, approaching their physical limits with any further increase in length proving extremely challenging to manufacturers. Significant strengthening of the joints, mountings and hinges between sections and along the boom adds cost both in terms of weight and bill of materials.